Navigational systems use map data to represent a map section on a display, for showing and determining routes, for destination input, for destination finding and for route guidance of a vehicle, such as a motor vehicle, steered by a driver.
These map data may be digital map data. In the map data, roads, for example, are shown as so-called edges, crossings or turn-offs of roads being shown as so-called knots. In this context, the real road pattern is approximated by the edges and knots, the edges being described, for instance, by a concatenation of straight-line edge sections. Thus, the representation of road networks is realized using directed graphs having edges and knots. Depending on the complexity of a crossing, it is described by a knot or even several knots. There may also be edges present within a crossing.
Digital maps may also be subdivided into individual regional partitions, so that the data that are to be loaded into the memory of, for instance, a navigational system may be delimited from the data set, since the data set influences the size of the memory required and the loading speed and the speed of processing. In a typical manner, the division of the map data into the partitions takes along lines of constant geographical length and width, so that approximately rectangular regions are defined as partitions. However, based on this subdivision, it is necessary to subdivide the edges which intersect one or more such boundaries between partitions, and to associate the subdivided edges with the respectively adjacent partitions or to store them redundantly in the adjacent partitions or to have them reported on by one of the participating adjacent partitions.
A subdivision of map data in partitions and a division of edges at partition borders is described in International Application WO 99/58934.
The division of the edges, however, causes additional data sets since, when an edge is divided, to connect the two partial edges, a knot of the map network has to be fitted in. This causes additional expenditure because of additional algorithmic steps, for instance, in response to the use of a navigational system for route calculation.
The redundant storage of the edges in several partitions has the disadvantage of leading to an increase in the data set. Also, in this case, when reading several partitions into one memory, the respective application has to ascertain the redundant edges and sort out edge data that are partially present several times, which also requires additional processor power, and consequently slows down the overall process.
The reporting of elements of other partitions has the disadvantage that more data have to be loaded into the memory than are currently needed, as, for instance, for representing maps, not only those partitions have to be loaded into the memory which are to be displayed, but all those partitions have to be loaded into the memory to which a report refers.